Light emitting diode (“LED”) devices are useful for generating light output. LED devices may convert electricity into photonic emissions more efficiently than incandescent and fluorescent bulbs. There accordingly are potentially great benefits, including energy conservation benefits, to LED utilization for lighting and other photonic applications. Further, as solid state devices, LEDs may have a larger average lifetime of utilization than and often are more resistant to physical damage than are conventional incandescent and fluorescent bulbs.
An LED may be positioned in a concave base housing and provided with anode and cathode bonding wires, placing the LED in communication with an electrical circuit for supplying a bias voltage to the LED. The LED may then be encapsulated in a material suitable to protect the LED from external contaminants and from being physically damaged or dislodged, and to form part of a lens system for focusing the light output of the LED. As an example, epoxy resin is often selected as the encapsulant, due to its useful material properties including hardness, resistance to chemicals, good adhesion to diverse materials, and good optical properties. The epoxy resin may be applied in the form of a liquid casting or molding composition. After the epoxy resin composition cures to form a solid polymer encapsulant, the LED device may be connected to an external circuit, and a bias voltage may be applied to the LED to generate light. The light generated by such an LED device may be intense, and substantial heat may also be generated. Extended exposure of the epoxy polymer resin encapsulant to light emitted by the LED, such as ultraviolet light, may cause molecular degradation of the epoxy polymer resin. Thermal cycling of the LED device as it is repeatedly activated to generate light and then allowed to cool may also cause heat degradation of the epoxy polymer resin encapsulant. Heat degradation may include further molecular degradation of the epoxy polymer resin, as well as mechanical degradation of the LED device itself due to repeated expansion and contraction of the encapsulant body having an embedded LED and bonding wires, since the encapsulant body may be juxtaposed with a concave base housing and other device elements that may have very different coefficients of thermal expansion.
In an effort to overcome the drawbacks of a permanent, solid epoxy polymer resin encapsulant, LED devices have been made using a liquid encapsulant housed in a suitable containment element. As an example, silicone liquids and silicone oils have been so used. However, these silicone encapsulants may have high coefficients of thermal expansion. Repeated heat cycling of the LED device accordingly may generate corresponding cycles of expansion and contraction of the liquid encapsulant. These cycles may in turn cause expansion and contraction of the containment element. The consequent stress applied to the other elements of the LED device, such as a concave base housing, may cause cracking and eventual failure of elements of the LED device, including the containment and base housing elements.
Therefore, as LED devices are implemented for diverse end use applications, there is a continuing need to provide LED device structures permitting the use of liquid encapsulants and having improved containment for such encapsulants.